1. Field of the Invention
The present invention relates to a technical field of a line driver and, more particularly, to a line driver with active termination.
2. Description of Related Art
In wired communication systems, a transmission line is commonly used to transmit signals while a line driver is used to drive the transmission line. The typical line driver can be either a voltage mode driver or a current mode driver. FIG. 1A shows a conventional voltage mode line driver. In order to reduce the reflection and energy loss of a transmitting signal, a resistor Rs is required to provide the impedance matching. When Rs=RL, the reflecting signal is minimum and the power transfer is maximum. The magnitude of the signal outputted from the voltage mode line driver 10 has to be double to the signal transmitted on the transmission line because of the impedance matching resistor Rs. Therefore, a voltage source for providing higher voltage power is needed to be the power supply for the driver 10.
FIG. 1B shows a conventional voltage mode line driver which is the improvement of the conventional voltage mode line driver shown in FIG. 1A. In FIG. 1B, Rs′=0.1*Rs and a voltage gain of a voltage amplifier has a voltage gain of 10. Due to the voltage gain of 10 in the voltage amplifier 20, an equivalent output impedance is 10*Rs′=10*0.1*Rs=Rs and thus the performance of the original impedance match is achieved. However, a voltage amplifier 20 and two resistors Ra and Rb are needed in the conventional voltage mode line driver shown in FIG. 1B. The amplifier in FIG. 1B is a non-inverting type amplifier. The linearity requirement of the operation range of the non-inverting type amplifier is strictly. Thus, the circuit design of the non-inverting type amplifier is complicated. The voltage amplifier 20 needs a wider single gain bandwidth to maintain the stability of the circuit.
Therefore, it is desirable to provide an improved line driver with active termination to mitigate and/or obviate the aforementioned problems.